1. Field of the Invention
Embodiments described herein relate generally to a method for acquiring a settling time and, for example, relates to a method for acquiring a settling time of an amplifier for deflection that deflects an electron beam of an electron beam writing apparatus.
2. Related Art
A lithography technique which leads development of micropatterning of a semiconductor device is a very important process for exclusively generating a pattern in semiconductor manufacturing processes. In recent years, with an increase in integration density of an LSI, a circuit line width required for semiconductor devices is getting smaller year by year. In order to form a desired circuit pattern on such semiconductor devices, a high-precision original pattern (also called a reticle or a mask) is needed. In this case, an electron beam (EB) pattern writing technique has an essentially excellent resolution, and is used in production of precise original patterns.
FIG. 11 is a conceptual diagram for explaining an operation of a variable-shaped electron beam writing apparatus. The variable-shaped electron beam writing apparatus operates as described below. A rectangular opening 411 to form an electron beam 330 is formed in a first aperture plate 410. A variable-shaped opening 421 to shape the electron beam 330 having passed through the opening 411 of the first aperture plate 410 into a desired rectangular shape is formed in a second aperture plate 420. The electron beam 330 irradiated from a charged particle source 430 and having passed through the opening 411 of the first aperture plate 410 is deflected by a deflector and passes through a portion of the variable-shaped opening 421 of the second aperture plate 420 before being irradiated on a target object 390 placed on a stage continuously moving in a predetermined direction (for example, an X direction). That is, a rectangular shape capable of passing through both the opening 411 of the first aperture plate 410 and the variable-shaped opening 421 of the second aperture plate 420 is written in a pattern writing region of the target object 340 placed on the stage continuously moving in the X direction. The method for forming any shape by causing a beam to pass through both the opening 411 of the first aperture plate 410 and the variable-shaped opening 421 of the second aperture plate 420 is called the variable-shaped beam method (VSB method).
In a writing apparatus, a pattern is written by deflecting a charged particle beam such as an electron beam by a deflector, and a DAC (digital/analog converter) amplifier is used for the deflection. Roles of beam deflection using such a DAC amplifier include, for example, control of the shape or size of a beam shot, control of a shot position, and blanking of a beam. To deflect a beam, it is necessary to set a settling time of a DAC amplifier needed to deflect a set amount of movement without error. If the settling time is not sufficient, an error occurs in the deflection movement amount. On the other hand, if the settling time is too long, throughput deteriorates. Thus, it is desirable to set as short a settling time as possible within a range in which no error occurs.
With development of more precise and finer circuit patterns typified by semiconductor devices in recent years, higher precision in pattern writing and improved throughput are also demanded from an electron beam writing apparatus. Thus, even slight position variations of a pattern written to a desired position on a mask by the above beam deflection affect dimensional precision for fabricating a semiconductor circuit. Thus, the above settling time needs to be optimized in the beam deflection using a DAC amplifier, particularly for control of the shot position. Conventionally, the settling time has been set, after measuring a pattern writing position using a position measuring device, in such a way that position displacements do not arise within a range measurable by the position measuring device (see Japanese Patent Application Laid-Open No. 2010-74039, for example).
However, with increasing micropatterning with higher precision in the future, the precision of calculation by the evaluation technique of the settling time described above is no longer sufficient.